Cytology of hermaphroditism in Icerya purchasi (Coccidae)

Summary

• 1. The California race of Icerya purchasi comprises only protandric hermaphrodites and males. There exist no pure females.

• 2. There is never any trace of parthenogenetic development of the eggs. Each egg must be fertilized by a spermatozoon in order to initiate development.

• 3. The eggs are usually fertilized by spermatozoa from the hermaphrodite's own testes; that is, the hermaphrodites are self-fertilizing.

• 4. Self-fertilized hermaphrodites give rise to hermaphrodites only.

• 5. Cross-fertilized hermaphrodites, i. e., those that have copulated with males, may give rise to broods of hermaphrodites only, or to mixed broods containing a small proportion of males.

• 6. It is therefore suggested that only in the rare instances when a male-producing spermatozoon from a pure male succeeds in fertilizing an egg in competition with the hermaphroditically produced spermatozoa docs a pure male result.

• 7. The morphology and histology of the hermaphroditic gonad is described for each of the nymphal and adult instars.

• 8. The somatic and oogonial chromosome number in the hermaphrodites is four. The eggs undergo a normal maturation. Two tetrads are evolved and two polar bodies given off, thus reducing the chromosome number to two. No indication of the peculiar behaviour reported by Pierantoni in the maturing egg was found.

• 9. Many entire spermatozoa enter each egg, and evolve nuclei which show the haploid chromosome group. These nuclei develop no further unless union with the female pronuclcus takes place. Fusion of the female pronucleus with one of the male pronuclei may take place at any point between the periphery and the center of the egg.

• 10. In the eggs of self-fertilized hermaphrodites, i. e., those which had been isolated from males since birth, and in the eggs of cross-fertilized hermaphrodites which had copulated with males, the processes of oogenesis and fertilization arc exactly the same. There is no way to distinguish the spermatozoa of the hermaphrodite from those of the true male in fertilization.

• 11. Spermatogenesis is in every respect the same in the testes of male and of hermaphrodite. The somatic and spermatogonial chromosome number is four. Two tetrads are evolved and a normal reduction takes place. The cytoplasmic division is invariably suppressed during the second maturation division, and may also sometimes be absent during first division. Thus two kinds of spermatids are produced, binucleate and quadrinucleate, whose components separate upon reaching maturity.

• 12. Incidental observations confirm Pierantonis claim that the mycetocytes in Icerya arise from simple cleavage cells.